As used herein, the term "electrical module" is intended to include any component, such as a semiconductor chip, a light emitting or detecting device, an emitting or detecting device of magnetic nature, a magnetic storage device, a capacitor, an inductor, a resistor, a crystal, a coil, a varactor, a thermistor, a resonator, transformers, and/or a connector that may be connected in an electrical circuit, an electro-optical circuit, an optical configuration, an electro-magnetic circuit and/or a magnetic configuration. The term "printed circuit board" is intended to encompass a support member that may be rigid or flexible, laminated or not, of any suitable composition, and that includes an electrically insulative surface on which a printed pattern of electrical conductors is provided. The term "printed pattern" is intended to encompass a pattern on a substrate formed by any suitable process, including, but not limited to, silk screen printing, photolithography, evaporation, plating, stenciling, ink writing, plasma deposition, sputtering, adhesives, or thin film or thick film techniques.
A printed circuit board having a semiconductor chip or other electrical module attached thereto shall be denoted as a printed circuit board assembly. It will be convenient to generally discuss the invention with particular reference to a printed circuit board assembly including a semiconductor chip of the surface mount or flip-chip type.
Such a chip typically has formed thereon an integrated circuit containing a number of electrical contacts (terminals) on one surface. The contacts are typically soldered or otherwise electrically connected to the conductors of the printed circuit board.
In the past, much effort has been focused on the use of conductors that are firmly adherent to the printed circuit board to minimize possible separation during use. Additionally, effort has also focused on maintaining the integrity of the conductor-chip interface to prevent failure at that connection. This arrangement usually operates satisfactorily. However, there are hostile environments, usually of high temperature and thermal excursions, where, during use, severe stresses cause the chip to separate from the printed circuit at or near the points of connections, i.e., the solder joints. Such stresses can occur, for example, when the printed circuit board is used in an automobile.
It is desirable to have conductors of compositions which result in a printed circuit board assembly in which the electrical modules remain reliably connected to the printed conductors in hostile environments.